Ute Risse-Buhl

Technische Universität Kaiserslautern & Campus Landau

Heterotrophic microbial decomposers colonize submerged leaf litter in close spatial proximity to periphytic algae that exude labile organic carbon during photosynthesis. These exudates are conjectured to affect microbial decomposers’ abundance, resulting in a stimulated (positive priming) or reduced (negative priming) leaf litter decomposition. Yet...

Climate change and erosion from agricultural areas cause increased drying periods and bedform migration of riverbeds, respectively, worldwide. Both sediment drying and bedform migration can independently stress the microbial community residing in the riverbed. Here, we investigated the microbial response after exposure to these stressors with a foc...

The bed of fluvial ecosystems plays a major role in global biogeochemical cycles. All fluvial sediments migrate and although responses of aquatic organisms to such movements have been recorded there is no theoretical framework on how the frequency of sediment movement affects streambed ecology and biogeochemistry. We here developed a theoretical fr...

Stream sediments move at low flow forming migrating ripples. These ripples can cover substantial areas where benthic communities experience erosion-resting cycles of sand grains. Sediment surface and interstitial space is colonized by meiobenthos, an assemblage of microscopic invertebrates. Here we describe how sediment migration influences the str...

On their way from inland to the ocean, flowing water bodies, their constituents and their biotic communities are exposed to complex transport and transformation processes. However, detailed process knowledge as revealed by Lagrangian measurements adjusted to travel time is rare in large rivers, in particular at hydrological extremes. To fill this g...

Epibenthic biofilms are important in regulating nitrogen (N) fluxes in stream ecosystems. The efficiency of the regulation is controlled by hydraulic and biological processes and their interactions. However, knowledge on the underlying physical and biological processes, their controlling parameters, and interactions in stream ecosystems is still li...

Nitrogen (N) uptake is a key process in stream ecosystems that is mediated mainly by benthic microorganisms (biofilms on different substrata) and has implications for the biogeochemical fluxes at catchment scale and beyond. Here, we focused on the drivers of assimilatory N uptake, especially the effects of hydromorphology and other environmental co...

Surface-groundwater interactions in intermittent rivers and ephemeral streams (IRES), waterways which do not flow year-round, are spatially and temporally dynamic because of alternations between flowing, non-flowing and dry hydrological states. Interactions between surface and groundwater often create mixing zones with distinct redox gradients, pot...

Sandy streambeds are mobile even at low flow velocities at which sediments can be transported as bedload, more specifically as migrating ripples. Small variations in discharge can result in transitions between sediment transport and no-transport. Despite being inherent processes of streams and rivers, the effect of sediment transport and transport...

Meeting ecological and water quality standards in lotic ecosystems is often failed due to multiple stressors. However, disentangling stressor effects and identifying relevant stressor-effect-relationships in complex environmental settings remain major challenges. By combining state-of-the-art methods from ecotoxicology and aquatic ecosystem analysi...

Biofilm activities and their interactions with physical, chemical and biological processes are of great importance for a variety of ecosystem functions, impacting hydrogeomorphology, water quality and aquatic ecosystem health. Effective management of water bodies requires advancing our understanding of how flow influences biofilm-bound sediment and...

Flow is an important physical driver of biofilm communities. Here, we tested the effects of the near bed flows in two mountainous stream reaches on the structure of biofilm microbial guilds (autotrophs, heterotrophic bacteria, and heterotrophic protists) within and across trophic levels. Near bed flow velocity and turbulent kinetic energy were impo...

A key research aim for lotic ecosystems is the identification of natural and anthropogenic pressures that impact ecosystem status and functions. As a consequence of these perturbations, many lotic ecosystems are exposed to complex combinations of non‐chemical and chemical stressors. These stressors comprise temperature fluctuations, flow alteration...

Multiple stressors pose potential risk to aquatic ecosystems and are the main reasons for failing ecological quality standards. However, mechanisms how multiple stressors act on aquatic communities and their functioning are poorly understood. This is especially true for two important stressors types, i.e. hydrodynamic alterations and toxicants. Her...

The objective of this study was to determine oxygen fluxes and the spatial micro-heterogeneity of microbial respiration and photosynthesis of a stream biofilm from the Selke stream, Harz Mountains. For this purpose, we used PreSens fiber optic O2 microsensors and an Automated Micromanipulator system to record O2 micro-gradients within the biofilm a...

Microbial diversity and function in intermittent rivers and ephemeral streams (IRES) are tightly linked to specific habitat availability and hydrological phases. The intensity and frequency of the different phases (especially drying and rewetting) affect community composition and key functions, mainly linked to biogeochemical processes. Resistance...

Input of allochthonous leaf litter is the main carbon source for heterotrophic metabolism in low-order forested streams. A major part of this leaf litter is accumulated at benthic retention structures or buried in the hyporheic zone. As a result of hyporheic sediment characteristics, hyporheic physicochemistry differs from that of the benthic zone...

Previous laboratory and on-site experiments have highlighted the importance of hydrodynamics in shaping biofilm composition and architecture. In how far responses to hydrodynamics can be found in natural flows under the complex interplay of environmental factors is still unknown. In this study we investigated the effect of near streambed turbulence...

Dieses Kapitel gibt einen Überblick über die limnologische Forschung in Jena. Es geht um die Angliederung der Limnologischen Arbeitsgruppe, unter Leitung von Dr. habil. Wilfried Schönborn, an das Institut für Ökologie der Friedrich-Schiller-Universität in Jena und die Weiterführung der Arbeitsgruppenleitung durch PD Dr. Heike Zimmermann-Timm. Es is...

Transient storage zones can be locations of intensive biogeochemical processing in streams, enhancing reach-scale nutrient uptake and metabolism. Despite this, the relationship between stream morphology, solute transport, nutrient cycling, and ecosystem functioning remains largely unresolved. We investigate the influence of stream channel morpholog...

1. The transformation of leaf litter, a key process in aquatic systems, is known to be reduced with decreasing oxygen concentrations, mainly due to lower abundance of and/or less active shredding macroinvertebrates. Aquatic fungi and phagotrophic protists involved in leaf litter processing can tol- erate low oxygen, but little is known about their...

Phagotrophic protist diversity in oligotrophic soils such as alpine glacier forefields is still poorly studied. Combining morphologic observations with molecular-based analyses, we assessed the diversity of major phagotrophic protist groups in two contrasting glacier forefields in the Swiss Alps (Tiefen glacier forefield, siliceous bedrock, and Wil...

The dynamics of dissolved organic carbon (DOC) have been intensively studied in mature ecosystems, but little is known about DOC dynamics and the significance of DOC as a substrate for microbial activity in earlysuccessional catchments. We determined the concentration, chemical composition, source, radiocarbon age, and bioavailability of DOC along...

The dynamics of dissolved organic carbon (DOC) have been intensively studied in mature ecosystems, but little is known about DOC dynamics and the significance of DOC as a substrate for microbial activity in early-successional catchments. We determined the concentration, chemical composition, source, radiocarbon age, and bioavailability of DOC along...

To clarify the structure of microbial food webs in groundwater, knowledge about the protist diversity and feeding strategies is essential. We applied cultivation-dependent approaches and molecular methods for further understanding of protist diversity in groundwater. Groundwater was sampled from a karstified aquifer located in the Thuringian Basin...

Aquatic heterotrophic protists structure biofilm morphology and stimulate organic matter processing, but knowledge about their effects on the activity of surface-associated communities is still missing. Microcosm experiments revealed that the community respiration of young biofilms (7 d old) at mineral surfaces was not affected by co-cultivation wi...

Food webs in the rhithral zone rely mainly on allochthonous carbon from the riparian vegetation. However, autochthonous carbon might be more important in open canopy streams. In streams, most of the microbial activity occurs in biofilms, associated with the streambed. We followed the autochthonous carbon transfer toward bacteria and grazing protozo...

The effect of Dexiostoma (filter feeder), Vannella, Chilodonella (raptorial feeders), Spumella, and Neobodo (direct interception feeders) on the morphology of multispecies bacterial biofilms was investigated in small flow cells. The filter feeder Dexiostoma campylum did not alter biofilm volume and porosity but stimulated the formation of larger mi...

Though seldom investigated, the microcurrent environment may form a significant part of the ecological niche of protists in stream biofilms. We investigated whether specific morphological features and feeding modes of ciliates are advantageous for a delayed detachment at increased flow velocities. Three sessile filter feeders (Vorticella, Carchesiu...

The impact of flow velocity on initial ciliate colonization dynamics on surfaces were studied in the third order Ilm stream (Thuringia, Germany) at a slow flowing site (0.09ms(-1)) and two faster flowing sites (0.31ms(-1)) and in flow channels at 0.05, 0.4, and 0.8ms(-1). At the slow flowing stream site, surfaces were rapidly colonized by ciliates...

Cross-barriers such as small dams cause local flow velocity heterogeneities, which might affect the formation, structure, and function of biofilms. The main objective of this thesis was to investigate the impact of flow velocity on colonization dynamics, grazing activity, and behavioral changes of biofilm associated ciliates. In addition, the effec...

A detailed assessment of degradation issues is essential for the development of reasonable restoration strategies. The assessment may be a difficult task when fluxes of organic matter and energy are concerned, which are primarily mediated by microorganisms. In small streams, biofilms are hot spots of trophic interactions. Small weirs cause small-sc...